Smoltification of Atlantic salmon in different water qualities and subsequent growth in sea water, following distinct transfer strategies from freshwater
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Atlantic salmon parr were kept in four different fresh water qualities for seven months before smoltification, which was characterized by plasma chloride content after sea water challenge tests. Three groups were transferred directly to sea water, together with three comparable subgroups, which had stayed the last seven weeks in a tank with increased water flow and fish density. Growth and mortality of all groups were thereafter followed for six months in sea water. Groups from fresh water with highest oxygen content and water exchange rate increased their biomass 5-6 times in sea water, whereas fresh water groups with low oxygen content and low water exchange rate only increased biomass 2-3 times in sea water. Mortality explained most of the differences in biomass. This emphasizes the importance of fresh water quality for the following success in sea water. Transference to new environmental conditions with increased fish density, water flow and exchange rate seven weeks ahead of release into sea water, had negative influence on the subsequent success in sea water. Smoltification in oxygen supersaturated (118 %) water had no negative influence on smolt quality.